Baffling Volume Increase

[picornavirus]

I had this high school project and my experiment involves using coconut water as a culture medium.

 

what perplex me is that when i add agar-agar to coconut water the volume increase?!

 

-what i do know from what my chemistry teacher told us is that when you add more mass it won't increase the volume but the density will increase

 

In my experiment, i had to make a ratio for the right mix not too soft and not to hard

 

the manufacturer's instructions said mix 90 g of agar-agar into 400 ml of water

Hench to make 1000 ml media i use a basic ratio and portion formula

 

M₁/V₁ = M₂/V₂

 

90g/ 400ml X n/1000ml

 

(90 g X 1000 ml) / 400 ml = 225 g

 

thus i added 225 g agar- agar to 1000 ml coconut water but what happened next disappoints me,

the volume increased it went way over the 1000 ml mark in my Erlenmeyer flask, but i still proceed with it.

it remained to be over 1000 ml mark after cooling it to room temp and worst of all the coconut agar was too soft

 

The next idea i had was to subtract 1000 mL and 225 g

so tried i subtracted 1000 by 225 and gave me 775

giving me a ration of 1:3.4

 

(density of coconut water is about 1.02 g/mL at 20 deg. Celsius basically it's near the density of water 1.0 g/mL

http://www.fruits-journal.org/articles/fruits/pdf/2012/03/fruits120009.pdf)

 

Hench i used 225 g of agar -agar and mixed it with 775 ml of coconut water

 

i did just that and it gave me a little below the 1000 mL mixture maybe around 990-999 mL. After heating, the media cooled and solidified they way i wanted not to soft and not to hard

 

I'm already finished with this project and my teachers never question the ratio i pulled out they just focused if i could grow things on it, i even got an A +

 

been weeks after that but it's still on my mind. It seems to break the laws of physics, it's too surreal because

the mass of the agar-agar added on to the coconut water what happen its like 225 g + 775 mL = about 1000 mL medium but not exactly 1000 mL

 

is that even possible? is there other laws behind it? i do know solvent increase the volume of the solute but not that significant unlike the case here.

 

 

 

I didn't have any pure cultures of any organisms to grow so i used banana, orange fruit peels, and leaves

results was a lot of fungi and yeast grew on it

 

sorry i have no pictures of it.

and sorry if bad english it's not my1st language

Edited February 10, 2016 by picornavirus

[fiveworlds]

-what i do know from what my chemistry teacher told us is that when you add more mass it won't increase the volume but the density will increase

 

Your chemistry teacher is wrong. You would expect that when you pour a into b you get a+b. However everything is composed of tiny particles so when you mix two different materials together the particles can move into gaps. This means that you won't get a volume anything like a+b. Like in this video with the sand just on a much smaller scale.

 

[Strange]

Doesn't that mean the teacher is right: "what my chemistry teacher told us is that when you add more mass it won't increase the volume" ?

 

I assume the answer to the question is something to do with the way the molecules of agar-agar form a gel, rather than dissolving (and so don't exploit the gaps between molecules of water). But I don't really know.

[hypervalent_iodine]

Doesn't that mean the teacher is right: "what my chemistry teacher told us is that when you add more mass it won't increase the volume" ?

 

I assume the answer to the question is something to do with the way the molecules of agar-agar form a gel, rather than dissolving (and so don't exploit the gaps between molecules of water). But I don't really know.

I would think this is the case.

 

OP, freezing water is probably a good illustrative example of what Strange is getting at. When you freeze water, the water molecules have to arrange in such a way that means they end up being well ordered and further apart than they would be in the liquid state. Thus, the volume of water increases (IIRC, by about 10%) when it becomes a solid. I realise that you don't change the mass in this example, but the principle is the same.

 

You could also consider it with these images:

 

 

 

The top one would contain more triangles per unit area than the bottom and thus occupy less volume, but both are otherwise the same. The only difference is how they are ordered.

 

As Strange has mentioned, you are not simply dissolving the agar, you are making a gel. The internal structure of the gel matrix in the coconut water is different to what it is with just the coconut water, and may cause the liquid to expand. This doesn't break any laws of physics.

 

(Sorry about the image sizes, I don't have the time to change it at the moment)